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11 package chapter7;
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13 import java.io.IOException;
14 import java.security.Principal;
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16 import javax.servlet.Filter;
17 import javax.servlet.FilterChain;
18 import javax.servlet.FilterConfig;
19 import javax.servlet.ServletException;
20 import javax.servlet.ServletRequest;
21 import javax.servlet.ServletResponse;
22 import javax.servlet.http.HttpServletRequest;
23 import javax.servlet.http.HttpSession;
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25 import org.slf4j.MDC;
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50 public class UserServletFilter implements Filter {
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52 boolean userRegistered = false;
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54 private final String userKey = "username";
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56 public void destroy() {
57 }
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59 public void doFilter(ServletRequest request, ServletResponse response,
60 FilterChain chain) throws IOException, ServletException {
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62 HttpServletRequest req = (HttpServletRequest) request;
63 Principal principal = req.getUserPrincipal();
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67 if (principal != null) {
68 String username = principal.getName();
69 registerUsername(username);
70 } else {
71 HttpSession session = req.getSession();
72 String username = (String)session.getAttribute(userKey);
73 registerUsername(username);
74 }
75
76 try {
77 chain.doFilter(request, response);
78 } finally {
79 if (userRegistered) {
80 MDC.remove(userKey);
81 }
82 }
83 }
84
85 public void init(FilterConfig arg0) throws ServletException {
86 }
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88 private void registerUsername(String username) {
89 if (username != null && username.trim().length() > 0) {
90 MDC.put(userKey, username);
91 userRegistered = true;
92 }
93 }
94
95 }